The present invention generally relates to a misfiring detecting method and apparatus for detecting the occurrence of misfiring in an internal combustion engine. More particularly, the present invention is concerned with a method and apparatus for detecting the occurrence of misfiring on the basis of a change in angular acceleration of the crankshaft of an engine in a predetermined angular range across a predetermined crank position.
Misfiring is a phenomenon which occurs in an internal combustion engine when at least one of the cylinders of the engine fails to ignite. Misfiring can be due to a number of causes, such as the failure of an ignition system to produce an adequate spark in a cylinder or the failure of a fuel supply system to supply a proper amount of air/fuel mixture to a cylinder. When misfiring is due to a failure of the ignition system, uncombusted fuel will be discharged from the misfiring cylinder. The discharge of uncombusted fuel is of course undesirable, because it can cause environmental pollution or a catalytic converter of the engine may be damaged. Therefore, it is desirable to detect misfiring in an engine and then cut off the supply of fuel to a misfiring cylinder.
For this reason, various misfiring sensing or detecting methods have been proposed, a typical one of which is disclosed in Japanese Published Unexamined Patent Application No. 62-26345 (JP-A-62-26345). According to this known method, pressure within each cylinder of an engine is constantly monitored by a pressure sensor, and the crankshaft angle at which a maximum pressure prevails in each cylinder is determined. When the maximum pressure for each cylinder falls within a prescribed period defined by two crank angles, the engine is considered to be operating normally.
The known method and apparatus, however, suffer a number of shortcomings. For example, it is necessary to continuously monitor the cylinder pressure, so the system structure tends to be complicated. Furthermore, when the engine is operating under a light load, the pressure in each cylinder has two peaks, one occurring at top dead center during the compression stroke and the other occurring during the combustion stroke, and it is difficult to discriminatively identify the two peaks. Besides, when a pressure peaks occurs prior to top dead center during the compression stroke of a cylinder, it is not possible to detect misfiring.